In high bit rate fiber-optic communication systems, chromatic dispersion in transmission fibers is a critical distance-related factor impeding the quality of propagating optical data signals and, as such, a length of fiber-optic spans.
Chromatic dispersion is a property of an optical fiber that causes different wavelengths propagate along the fiber at different speeds. As any signal has a certain spectral width, chromatic dispersion causes the signal becoming more and more distorted when the signal propagates along the fiber. Chromatic dispersion of a fiber may vary as the fiber ages or because of environmental factors, such as changes of temperature, atmospheric pressure, and the like.
Without special compensation techniques, chromatic dispersion imposes a limit on a transmission distance and a modulation bit rate of a fiber-optic communication system.
In a conventional fiber-optic communication system, data is transmitted through a transmission fiber at a fixed optical wavelength and the transmission fiber is associated with one or more dispersion compensation modules (DCMs) disposed at terminals of the system. To provide efficient compensation of chromatic dispersion in the transmission fiber, a large quantity (or granularity) of DCMs having incremental fixed amounts of chromatic dispersion or dispersion-controlled DCMs should be available.
The chromatic dispersion of optical fibers is a function of the wavelength. In conventional systems, the wavelength dependency of the DCM is selected to either cancel or reduce to an acceptable level the chromatic dispersion of the transmission fiber over the wavelength band of interest.
However, such means of compensating chromatic dispersion add to already high complexity and high cost of the fiber-optic communication systems.